Re: [Qemu-devel] [PATCH 1/1] seqlock: Fix warning reg. incompatible cast

[Paolo Bonzini <pbonzini@redhat.com>]

On 07/08/2016 03:41, Pranith Kumar wrote:
> With the latest clang, we have the following warning. We are not using
> the const qualifier consistently in other functions. So remove it from
> the only one that uses it to fix the warning.
> 
> /home/pranith/devops/code/qemu/include/qemu/seqlock.h:62:21: warning: passing 'typeof (*&sl->sequence) *' (aka 'const unsigned int *') to parameter of type 'unsigned int *' discards qualifier
> s [-Wincompatible-pointer-types-discards-qualifiers]
>     return unlikely(atomic_read(&sl->sequence) != start);
>                     ^~~~~~~~~~~~~~~~~~~~~~~~~~
> /home/pranith/devops/code/qemu/include/qemu/atomic.h:58:25: note: expanded from macro 'atomic_read'
>      __atomic_load(ptr, &_val, __ATOMIC_RELAXED);     \
>                         ^~~~~
> /home/pranith/devops/code/qemu/include/qemu/compiler.h:62:43: note: expanded from macro 'unlikely'
> #define unlikely(x)   __builtin_expect(!!(x), 0)
> 
> Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>

This is a compiler bug, isn't it?  Atomic loads of a const pointer
should be allowed.

Paolo

> ---
>  include/qemu/seqlock.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/qemu/seqlock.h b/include/qemu/seqlock.h
> index 2e2be4c..aa4cf15 100644
> --- a/include/qemu/seqlock.h
> +++ b/include/qemu/seqlock.h
> @@ -55,7 +55,7 @@ static inline unsigned seqlock_read_begin(QemuSeqLock *sl)
>      return ret & ~1;
>  }
>  
> -static inline int seqlock_read_retry(const QemuSeqLock *sl, unsigned start)
> +static inline int seqlock_read_retry(QemuSeqLock *sl, unsigned start)
>  {
>      /* Read other fields before reading final sequence.  */
>      smp_rmb();
>